This invention relates to ceramic monolithic supports for catalysts and, in particular, to supports containing permanent inorganic binding materials which can be fired at low temperatures, imparting strength to the support while maintaining substantial surface area.
The conventional ceramic monolithic catalyst support consists of a ceramic support with a coating of a high surface material upon which the catalyst is actually deposited. In order to obtain substantial density and strength, the ceramic material normally must be fired at a high temperature. Such high-temperature firing, however, necessarily sinters the ceramic material and results in its having a very small surface area. Consequently, the ceramic must be coated with another material having a higher surface area, as well as specific chemical characteristics on which to actually deposit the catalyst. This procedure of depositing a high surface area "washcoat" on the low surface area ceramic wall is disclosed, for example, in U.S. Pat. Nos. 2,742,437 and 3,824,196.
In addition to requiring the second production step of applying the washcoat, catalyst supports of this kind suffer from several disadvantages in use. In service, the supports are exposed to a flow of gases which often contain dusts or particulate matter, which can cause the high surface area coating to flake off the underlying ceramic support. This phenomenom can also occur where the support is exposed to thermal cycling because the wash coat and the underlying ceramic material often have different thermal expansion coefficients.
It is therefore an object of the present invention to provide a monolithic support having a high surface area which is not easily abraded. It is a further object of the invention to provide a monolithic support which develops substantial strength at temperatures below those at which the high surface area of the constituent materials would be adversely affected.